(a). Field of the Invention
The invention relates to communication networks, and more particularly to a network system with quality of service (QoS) management and an associated QoS management method.
(b). Description of the Prior Arts
In recent years, the integrated circuit (IC) technology develops rapidly so that the System-on-Chip (SoC) approach is increasingly applied. The Network-on-Chip (NoC) architecture has also been developed to serve as the communication basis between system components. Since both the number of components and the need for bandwidth within a chip increase rapidly, the point-to-point standard protocol such as Open Core Protocol (OCP) or Advanced extensible Interface (AXI) is applied to the interface between the components so as to upgrade the working frequency and throughput of a NoC system. The physical layer of the NoC system utilizes point-to-point handshaking to control data flow and perform one-way phased transmission. The packet information provided by the standard protocol is used to facilitate data transmission and further provide the Quality of Service (QoS) function for data exchange. Packets, used for data exchange between the system components, may have different communication requirements depending on the involved components or tasks. For example, some of the packets need to be transmitted to their destination without too much delay so as to achieve a high data rate; the other packets may allow more delay in the transmission process.
FIG. 1 is an architecture diagram of a conventional NoC system 10, which includes switch units 11, 12 and 13, master devices 14, 15 and 16 and a slave device 17. The NoC system 10 adopts a multi-level, switch-to-switch structure wherein each switch unit forms a center of a cluster or communication sub-system, and one-way point-to-point shared signal paths 101, 102 and 103 respectively connect between the switch units 11 and 12, the switch units 12 and 13, and the switch unit 13 and the slave device 17, thereby transmitting packets across different levels. Since each switch unit may receive packets from multiple sources (including the master device and the switch unit at the previous level) at the same time and also the signal paths 101, 102 and 103 are shared, the switch unit should consider various communication requirements of the received packets so as to establish its packet arbitration policy for determining the forwarding sequence of the received packets. However, in the architecture of FIG. 1, when a lot of high priority packets crowd into the switch unit, it may cause collision of packet forwarding or even network congestion such that the forwarding of the high priority packets cannot meet QoS requirements of the system. Furthermore, since the high priority packet is forwarded in a higher priority than a low priority packet, the forwarding of the low priority packet may be delayed too much and thus cannot meet the QoS requirements either.